1. Field of the Invention
The invention relates to an auxiliary motor vehicle heater with a control device which has a connection for a voltage supply line which leads from the battery of the motor vehicle to the control device. Furthermore, the invention relates to a control device for such an auxiliary motor vehicle heater, a motor vehicle with such an auxiliary motor vehicle heater, and a process for operation of an auxiliary motor vehicle heater.
2. Description of Related Art
In this connection, a motor vehicle is defined as a vehicle which is provided with an engine, especially an internal combustion engine, and which can be driven by it. The engine is generally started with a starter which is connected to the battery. The battery is charged in engine operation by a generator which is also called a dynamo. These motor vehicles generally have a passenger space for a driver, and optionally, for passengers.
Auxiliary motor vehicle heaters are used as so-called auxiliary air heaters or auxiliary water heaters in motor vehicles, such as for example in passenger cars. They are generally used to heat the passenger compartment or to preheat the cooling water of the internal combustion engine of the motor vehicle.
During operation of an auxiliary motor vehicle heater, it is often advantageous if information is available in its control device about the operating state of the engine of the motor vehicle. Therefore, in known auxiliary motor vehicle heaters, a so-called terminal 15 on the control device is connected to the ignition signal line, via which the control device receives information xe2x80x9cengine ignition is turned on.xe2x80x9d The ignition signal line in the motor vehicle can be moved from the ignition lock in the passenger compartment to the control device of the auxiliary motor vehicle heater and there can be a connection at the terminal 15 on its control device. In control devices without a terminal 15, the required information cannot be determined so far.
German Patent DE 196 01 772 C2 discloses a process for starting an auxiliary motor vehicle heater, in which, proceeding from the initiation of the starting process by actuating the ignition lock of the motor vehicle (compare the aforementioned terminal 15), at least one temperature is checked. When a given theoretical temperature threshold is exceeded, starting of the auxiliary motor vehicle heater does not take place. Otherwise, during operation of the vehicle engine starter high-consumption assemblies, for example, the ignition means of the auxiliary motor vehicle heater, are turned off. This interruption of operation of high-consumption assemblies in motor vehicles is conventional. It is called xe2x80x9cundervoltage switching.xe2x80x9d It is thus ensured that starting of the engine by means of the starter is not endangered. Interruption of the assemblies takes place, as explained in German Patent DE 196 01 772 C2, using a voltage signal line which indicates the current voltage value of the motor vehicle battery. If the voltage value drops below a threshold, operation of the assembly is interrupted. Therefore, it is interrupted exactly when the battery voltage drops too far due to operation of the starter. If the battery voltage should be above the threshold value, even when the starter is in operation, there is no interruption of the starting process of the auxiliary motor vehicle heater. Finally, the starting process of the auxiliary motor vehicle heater is begun again when the generator of the motor vehicle is operated by the engine. To do this, a generator signal line is connected to the control device via a terminal 61 at which there is a positive signal in this case.
The primary object of the present invention is to provide an auxiliary motor vehicle heater which can be produced more economically than known systems of the initially mentioned type. In particular, information about the operating state of the engine will be made available to the control device of the auxiliary motor vehicle heater more easily.
This object is achieved in accordance with the invention with an auxiliary motor vehicle heater of the initially mentioned type in which the control device can detect the voltage characteristic on the connection for the voltage supply line and can determine the information xe2x80x9cstarting of the engine of the motor vehicle is completedxe2x80x9d depending on the voltage characteristic. Furthermore, the object is achieved with such a control device for an auxiliary motor vehicle heater and with a motor vehicle which is provided with such an auxiliary motor vehicle heater, and finally also with a process for operating an auxiliary motor vehicle heater with a control device with the following steps: detection of the voltage characteristic on a connection of the control device for the voltage supply line which leads from the battery of the motor vehicle to the control device, and determination of the information xe2x80x9cstarting of the engine of the motor vehicle is completedxe2x80x9d depending on this voltage characteristic.
In the control device of the auxiliary motor vehicle heater, the invention eliminates the above described connections for the voltage signal line, the generator signal line via the terminal 61 and also the ignition signal line via the terminal 15. The required information xe2x80x9cstarting of the engine of the motor vehicle is completed,xe2x80x9d in accordance with the invention, is made available in a much simpler manner by evaluation of the voltage characteristic on a voltage supply line which is present anyway on the control device.
The evaluation of the voltage characteristic can be integrated into the electronics of modem control devices by the corresponding programming and/or with a matched circuit. The complexity necessary for this purpose is low compared to the indicated connections or terminals on the control device and its cabling in the control device and with signal lines in the motor vehicle.
In an advantageous development of the invention, the control device determines the information xe2x80x9cstarting of the engine is completedxe2x80x9d when the voltage characteristic, proceeding from the first voltage value, has a drop and subsequent rise beyond this first voltage value. In contrast to the existing process of monitoring the battery voltage, according to the invention, it is not the fact that the voltage threshold has not been reached which is checked, but instead whether, after a drop of the voltage, it rises to a higher value than prevailed before the drop that is determined. This higher value allows the conclusion that, after the engine starter has been actuated, the engine is running and driving the generator which, for its part, charges the battery and produces the higher voltage. Thus, the voltage of the battery in a motor vehicle with a medium vehicle voltage of 12 V is roughly 12 V when the engine is off, drops dramatically when the starter is operated, and then rises during operation of the generator or dynamo to a value over 12 V, at maximum roughly to 14 V. Therefore, in this development of the invention, the voltage characteristic is examined not only with respect to the voltage drop, but also with respect to the voltage rise. The time relation and the relative change of the voltage during dropping and rising yields the required information xe2x80x9cstarting of the engine is completed.xe2x80x9d Solely evaluation of the voltage drop below a threshold value, as is described in DE 196 01 772 C2, would not be sufficient to make this information available.
In one alternatively or additionally reasonable development of the invention, the control device determines the information xe2x80x9cstarting of the engine is completedxe2x80x9d when the voltage characteristic has fluctuations which allow conclusions about the charging of the battery using the generator of the motor vehicle. In this connection, the fluctuation of the battery voltage is also called the residual ripple of the battery voltage or the ripple voltage. This takes place, by analogy to the residual AC voltage which is superimposed on the initial DC voltage of a power supply, in spite of filteringxe2x80x94residual ripple or ripple voltage is also addressed there. The residual ripple which is produced by the charging of the battery generally is regularly alternating and is measured by determining the distance of the highest and lowest value of the fluctuations. The fluctuations arise as a result of the magnetic rotary field in the generator. They have a relative fluctuation width of less than 1 V to 2 V.
The control device of the invention, in addition to use in an auxiliary motor vehicle heater, can also be used in other assemblies of the motor vehicle in which the information xe2x80x9cstarting of the engine of the motor vehicle is completedxe2x80x9d or xe2x80x9cengine is operatingxe2x80x9d is of interest. Thus, for example, control devices can also be equipped with monitoring of the voltage characteristic in accordance with the invention on a connection for the voltage supply line, as are provided in automatic transmissions, in sliding roofs or window raiser controls, in braking systems or in safety systems, such as belt tighteners and airbags.
One embodiment of an auxiliary motor vehicle heater in accordance with the invention is explained in detail below using the accompanying drawings.